Airstream had some good intentions in the 1970s when they decided to use dual pane windows (aka double pane). They installed dual pane windows in the front window, both front winged windows, and the upper vista view windows. The advantage of these windows is that they insulate much better than single pane due to the gas (typically argon or krypton) layer between the dual panes. This is similar to how a double walled air insulated coffee mug keeps your coffee hot much longer than a normal mug. Better insulation means better efficiency and reduced dependency on heating and cooling systems.
Table below is cost comparison to replace two vista view windows in a 1971 Airstream Globetrotter. Prices shown are estimates only and are from Oct 2014. Current prices may differ.